This invention pertains to vinyl chloride polymerethylene/vinyl alcohol copolymer barrier packaging compositions and in particular to those compositions having enhanced resistance to gas permeability and moisture vapor transmission.
Polyvinyl alcohol and its copolymers containing large amounts of hydroxyl groups are known to possess very low gas permeabilities. However, the use of such materials in packaging applications is severely restricted by moisture sensitivity imparted by the hydroxyl function. The gas permeabilities of polyvinyl alcohol homopolymer increase exponentially as a function of relative humidity. Copolymers of vinyl alcohol although somewhat less sensitive are still prone to this defect for packaging materials. Commercial standards for acceptable packaging materials require that the films used have a low gas permeability particularly to oxygen and in addition have a low moisture vapor transmission rate. One solution to this problem has been proposed in U.S. Pat. No. 3,585,177, issued to D. M. Gardner et al. on June 15, 1971, in which a lower alpha olefin/vinyl alcohol copolymer is prepared having a residual ester content below 3.0% and an olefin content between 5.0 to 40% by weight and wherein the differential thermal analysis curve for the copolymer is a single narrow endotherm having a melting range of less than 30.degree. C.
A more economical solution to the problem of providing suitable packaging materials having good barrier properties resides in blending cheaper resins with a balance of properties. This approach however is limited because of the problem of incompatability which exists between many available resins.